Abstract:BACKGROUND: Treatment options for HIV-1 infected individuals who have received extensive previous antiretroviral therapy are limited. We compared efficacy and safety of the novel non-peptidic protease inhibitor tipranavir co-administered with ritonavir plus an optimised background regimen with that of an investigator-selected ritonavir-boosted comparator protease inhibitor (CPI-ritonavir) in such patients. METHODS: We did a combined analysis of 48-week data from two ongoing, randomised, open-label, multinational, phase III, RESIST studies. HIV-1-infected adults with 3 months or longer previous triple antiretroviral class experience, two or more previous protease inhibitor regimens, HIV-1 RNA 1000 copies per mL or greater, and genotypically demonstrated primary resistance to protease inhibitor, were eligible. Primary endpoints were proportion of treatment responders (with reduction in viral load of 1 log(10) copies per mL or greater below baseline without treatment change) at 48 weeks and time to treatment failure through 48 weeks (intention-to-treat analysis). The RESIST studies are registered with ClinicalTrials.gov, numbers NCT00054717 (RESIST-1) and NCT00144170 (RESIST-2). FINDINGS: 3324 patients were screened; 746 received tipranavir-ritonavir and 737 CPI-ritonavir. 486 (65.1%) patients on tipranavir-ritonavir and 192 (26.1%) on CPI-ritonavir remained on assigned treatment until week 48. At week 48, more patients achieved and maintained treatment response in the tipranavir-ritonavir group than in the CPI-ritonavir group (251 [33.6%] vs 113 [15.3%]; p<0.0001). Median time to treatment failure was significantly longer in the tipranavir-ritonavir group than in the CPI-ritonavir group (113 days vs 0 days; p<0.0001). Gastrointestinal system disorders and raised transaminase, cholesterol, and triglycerides were more frequent in the tipranavir-ritonavir group than in the CPI-ritonavir group. INTERPRETATION: Compared with CPI-ritonavir, tipranavir-ritonavir with an optimised background regimen provides better virological and immunological responses over 48 weeks in patients who have received extensive previous antiretroviral treatment.